Basic angle facts

Edexcel marks all angle answers with reasons. A correct numerical answer with no reason loses 1 mark on every part. Use the standard wording from the mark scheme.

Angles at a point

Angles around a single point sum to 360°.

Reason wording: "angles around a point sum to 360°".

Angles on a straight line

Angles on one side of a straight line sum to 180°.

Reason wording: "angles on a straight line sum to 180°".

Vertically opposite angles

When two straight lines cross, opposite (vertically opposite) angles are equal.

Reason wording: "vertically opposite angles are equal".

Angles in parallel lines (transversal)

A transversal crossing two parallel lines creates three angle relationships:

1. Corresponding angles equal (same position relative to each parallel line; the "F-shape").
2. Alternate angles equal (opposite sides of the transversal, between the parallels; the "Z-shape").
3. Co-interior (allied) angles sum to 180° (same side of the transversal, between the parallels; the "C-shape").

Reason wording: "corresponding angles are equal", "alternate angles are equal", "co-interior angles sum to 180°" (or "allied angles").

Angles in a triangle

Sum to 180° ("angles in a triangle sum to 180°").

Angles in a quadrilateral

Sum to 360° ("angles in a quadrilateral sum to 360°").

Edexcel exam tip

Always give a reason alongside every angle calculation. The standard mark-scheme phrases are:

• "angles in a triangle sum to 180°"
• "angles around a point sum to 360°"
• "angles on a straight line sum to 180°"
• "vertically opposite angles are equal"
• "alternate angles are equal"
• "corresponding angles are equal"
• "co-interior angles sum to 180°"

Edexcel will accept any wording that clearly identifies the geometric fact. Avoid abbreviations like "vert opp" or "alt angles" — write them in full.